The radio network controller (RNC) is an important component in the third generation mobile communication wideband code division multiple access system (3G W-CDMA), which performs important functions such as access control of a radio network, management of radio resources, establishment and release of radio links, and the performance of which will directly decide quality of service that can be provided by the whole 3G W-CDMA system. Since a huge 3G network can only be built step by step, in order to ensure low cost and high efficiency of an initial investment of an operator and smooth extension of the 3G network, the RNC must have good extendibility.
However, in the current 3GPP Release 1999 protocol specification regarding W-CDMA, the RNC and other network elements in the 3G systems transmit information through ATM. Therefore, many equipment providers naturally adopt ATM switching mode. However, the ATM switch has many defects such as high cost, complex configuration and management, and hard to extend.
FIG. 1 describes features of the structure of an ATM switching based radio network controller. It can be seen from FIG. 1 that, the ATM switching based radio network controller comprises a multiplexing and interface module (MUX), an ATM switching model (Switching), a signaling processing unit (SPU), a data processing unit (DPU) and a resource control unit (RCU), wherein the MUX module performs an external interface function of the controller, the Switch module performs data exchange between the above units and maintain routing of the data exchange, the SPU module performs the processing of a signaling part of the protocol, the DPU module performs the processing of a data part of the protocol, and the RCU module performs a control function of radio resources and local resources of the controller, and is connected to an external operation, maintenance and management (O&M) equipment.
A common ATM switching has the following features: the ATM switching is connection oriented, and requires configuration and management operations such as node initialization and routing table maintenance; the ATM switching network is difficult to perform a multipoint transmission and broadcast function, and the ATM switching module (ATM switch) must use the routing table to determine a next output route and port of the information; the ATM route identification is network structure oriented, is determined by a virtual path identification (VPI) and a virtual channel identification (VCI), and needs to be configured and maintained. During information transmission, a header of each information element comprises the current route identification.
Generally, an ATM switching flow is that, a switching node extracts the route identification from a received information element, looks up the routing table to obtain the next route identification and the output port, changes the route identification in the header of the information element, and transmits the information element out from the output port. By taking the 3G protocol as an example, in a radio network controller using ATM technology, the operating principle of information exchange is shown in brief as follows:
RRC message flow:
Iub→MUX→Switch→DPU→Switch→SPU
NBAP/RANAP/RNSAP/ALCAP message flow:
Iub/Iur/Iu→MUX→Switch→SPU
Iub→Iur data flow:
Iub→MUX→Switch→DPU→Switch→MUX→Iur
Iub→Iu data flow:
Iub→MUX→Switch→DPU→Switch→MUX→Iu
The above information exchange flows will be respectively explained below:
1. RRC information exchange flow: after the RRC information coming from the Iub interface is received by the multiplexing and interface module (MUX), its route identification is exchanged and is transmitted to the ATM switching module (Switch); the Switching module exchanges the route identification and transmits the information to a specified data processing unit (DPU); the DPU module processes a user plane protocol and reroutes so as to re-transmit the information to the Switch module; the Switch module exchanges the route identification and finally transmits the information to the signaling processing unit (SPU).
2. RANAP information exchange flow: after the RANAP information coming from the Iu interface is received by the multiplexing and interface module (MUX), its route identification is exchanged and is transmitted to the ATM switching module (Switch); the Switch module exchanges the route identification and finally transmits the information to the signaling processing unit (SPU). NBAP, RNSAP and ALCAP information flows are the same as or similar to the RANAP information flow.
3. Iub to Iur information exchange flow: after the user data information coming from the Iub interface is received by the multiplexing and interface module (MUX), its route identification is exchanged and is transmitted to the ATM switching module (Switch); the Switch module exchanges the route identification and transmits it to a specified data processing unit (DPU); the DPU module processes the user plane protocol and reroutes so as to re-transmit the information to the Switch module; the Switch module exchanges the route identification and transmits it to the MUX module; MUX module exchanges routes and finally transmits the information to the Iur interface.
4. Iub to Iu information exchange flow, which is similar to the Iub to Iur information exchange flow, but finally transmits the information to the Iu interface.
When the above message flows or data flows are switched based on ATM, it is crucial to specify in the header of each data package, ID of PVC and its AAL2 or AAL5 as an index of the ATM switching.
It can be seen from the features of the ATM switching itself and the operating principle of ATM information exchange, the traditional radio network controller using ATM switching technology has the following defects: since an end-to-end connection needs to be established between ATM switching based processing units, the process of configuring, establishing and removing routes is complex and its switching network needs a lot of routing information to manage and maintain. In addition, it is very difficult to pack and unpack ATM information elements, such that each step of the switching flow has a certain complexity.
As to the extendibility, the ATM switching based radio network controller generally uses a single chassis, thus its extensibility is poor. Since the ATM switching mechanism is difficult to be achieved, even if a back-plate bus type is used, existing ATM switching products are generally used between multiple chassis. Since switching ports supported by these products are generally fewer, if they are cascaded by multiple layers, the switching routing configuration will be more complex and the operation and maintenance will be more difficult. For example, if the radio network controller is extended on the basis of the structure shown in FIG. 1, not only an extended switching interface block (SXB) is required to be added in each chassis, but also an external ATM switch is required to connect an elementary unit (chassis) with an extended unit (chassis). Since connecting end points have different features, the multiplexing and interface (an external interface of the RNC that is mainly user-network interface UNI) module cannot be identical with the extended switching interface (the internal extended interface of the RNC that is mainly network-network interface NNI), which further adds the complexity and processing difficulty of the switching routing in the ATM switching module within the chassis. When the number of the extended chassis increases, the complexity of the switching module in the chassis increases, thus routing configuration and management becomes a bottleneck of the extensibility and maintainability of the overall product. In addition, the use of external ATM switch or cascaded ATM switch having a large capacity also has the problem of complex configuration, which is also a factor to limit its extensibility.
Since the various processing modules (for example, SPU, MUX, SXB, and so on) cannot be implemented in a unified platform, the cost for implementing the processing modules is comparatively higher. Heretofore, the cost for implementing the ATM switching module or ATM switch is also comparatively higher and there is little choice in the market, thus the overall cost of the ATM switching based radio network controller is comparatively higher.
In summary, the radio network controller using the ATM switch is high in cost, complex in configuration and management and difficult to extend, all of which will affect the build of the future 3G network.